The modification of proteins by myristoylation is required for the subcellular targeting, protein conformation and biological activity of many important proteins in eukaryotic cells, including those required for signal transduction and regulatory functions important in cell growth (Towler et al. J Biol Chem 1987; 262:1030-6. 20: Wolven et al. Mol Biol Cell 1997; 8:1159-73.). The myristoylation reaction, the transfer of myristic acid from myristoyl-coenzyme A (CoA) to the amino groups of terminal glycine residues, is catalysed by the ubiquitously distributed enzyme N-myristoyl-CoA:protein, N-myristoyl transferase (NMT). The reaction requires only myristoyl-CoA and a protein containing a suitable peptide sequence, and occurs through an ordered Bi Bi mechanism. This modification occurs primarily as a cotranslational process (Wilcox et al. Science 1987, 238:1275-8. 22; Deichaite et al. Mol Cell Biol 1988; 8:4295-301), although myristoylation can also occur post-translationally (Pillai et al. Proc Natl Acad Sci USA 1987; 84:7654-8. 24: King et al. J Biol Chem 1989; 264:7772-5.).
N-myristoyltransferase (NMT) has been shown to be essential in the kinetoplastid protozoan parasites, Leishmania, Trypanosoma brucei and Plasmodium falciparum. The demonstration of essentiality by genetic studies in these parasites has been supported by limited chemical validation. Non-specific myristoyl CoA inhibitors inhibit T. brucei and Leishmania growth in culture. A screen of compounds developed as inhibitors of fungal NMT identified a number of inhibitors of both T. brucei NMT and T. brucei in culture. Screening of recombinant Plasmodium falciparum NMT has identified a series of benzothiazole analogues with IC50 values<50 μM, with selectivity over human NMT1. Two of compounds of the series when tested at a concentration of 10 μM against cultured parasites in vitro reduced parasitemia by >80%. (Bowyer et al., Biochemical Journal (2007), 408(2), 173-180.)
Two isozymes of the mammalian NMT enzymes, NMT1 and NMT2, have been cloned and share ˜77% identity (Giang D K, Cravatt B F. A second mammalian N-myristoyltransferase. J Biol Chem 1998; 273:6595-8.) with the majority of divergence occurring in the amino-terminal domains. Splice variants of NMT1 have also been observed in some cells. Possibly these amino-terminal variations allow differential cellular localization of the isozymes, thereby allowing either cotranslational ribosome-based or post-translational cytosol-based protein myristoylation. NMT1 and NMT2 have similar, but distinguishable, relative selectivity, as shown by an in vitro comparison of the activity of the isozymes on a limited panel of substrate peptides. (Giang and Cravatt, J Biol Chem 1998; 273:6595-8. 27; Aitken A, Biochem Soc Trans 1989; 17:871-5.).
The role of myristoylation is still being elucidated; however evidence of its involvement in many disease states, such as cancer (Selvakumar, P. et al., Progress in Lipid Res., 2006, (46), 1-36), epilepsy (Selvakhumar, P. et al., Biochem. Biophys Res. Comm. 2005, (335), 1132-1139), Alzheimer's disease, ischemia, diabetes, HIV (Shoji, S. et al., JP2006223173) and osteoporosis is growing. Cellular myristoylated proteins have diverse biological functions in oncogenesis and signal transduction. Examples include the catalytic subunit of cAMP4-dependent protein kinase, various tyrosine kinases (pp60src, pp60yes, pp56lck, pp59fyn/syn, and c-Abl), the α-subunit of calcineurin (Lakshmikuttyamma, A et al., Progress in Neurobiol. 2008, 84 (1), 77-84) the myristoylated alanine-rich C kinase substrate, and the α-subunit of several guanine nucleotide binding proteins and ADP ribosylation factors.
An increase in NMT activity and expression has been shown in a number of tumour types, suggesting inhibitors of NMT would be potential anti-cancer agents. In addition the Src family of tyrosine kinases (e.g., c-Src, Yes, and Fyn) are oncogenic proteins which require myristoylation in order for them to function in cells.
Functionally characterization of the two NMT isozymes in human cells using unique small interfering RNAs (siRNA) for each isozyme were shown to decrease NMT1 or NMT2 protein levels by at least 90%. Knockdown of NMT1 inhibited cell replication associated with a loss of activation of c-Src and its target FAK. Depletion of either NMT isozyme induced apoptosis, with NMT2 having a 2.5-fold greater effect than NMT1. Intratumoral injection of siRNA for NMT1 or for both NMT1 and NMT2 inhibited tumour growth in vivo, whereas the same treatment with siRNA for NMT2 or negative control siRNA did not. Overall, the data indicate that NMT1 and NMT2 have only partially overlapping functions and that NMT1 is critical for tumour cell proliferation. (Ducker et al., Mol Cancer Res 2005; 3(8). August 2005).
Viruses and bacteria usually lack N-myristoyltransferases so consequently their proteins are processed by NMTs of their eukaryotic hosts. (Maurer-Stroh et al., Trends in Microbiology (2004), 12(4), 178-185.) For example, human N-myristoyltransferase (hNMT) catalyzes N-myristoylation of several HIV-1 proteins, including Pr160gag-pol, Pr55gag, the capsid protein p17 derived from proteolytic processing of gag, and neg. factor (nef). N-myristoylation of Pr160gag-pol and Pr55gag is required for viral replication. Reduction in the mRNA levels of human NMT isoforms and NMT activities have been shown in the course of HIV-1 infection in the human T-cell line, CEM. In consequence, novel synthetic NMT inhibitors were significantly more cytotoxic to chronically HIV-1 infected T-cell line, CEM/LAV-1, compared to uninfected CEM cells. (Takamune et al., FEBS Letters (2002), 527(1-3), 138-142.)
Myristic acid analogues designed as alternative substrates for NMT have shown to inhibit the proliferation of HIV-1 (Bryant et al., Perspectives in Drug Discovery and Design (1993), 1(1), 193-209.; Devadas et al., Bioorganic & Medicinal Chemistry Letters (1993), 3(4), 779-84.) and Hepatitis B (Parang et al., Antiviral Research (1997), 34(3), 75-90.) In addition myristic acid analogues have been shown to inhibit HIV-1 (Adams et al., Eur. Pat. Appl. (1992), 20 pp. EP 480901 A1) and Varicella Zoster virus replication (Gilbert et al., Antiviral Chemistry & Chemotherapy (1994), 5(3), 182-6.).
NMT has been shown genetically to be essential for a number of fungal strains, such as Candida albicans (Weinberg et al., Molecular Microbiology (1995), 16(2), 241-50.), Saccharomyces cerevisiae, Cryptococcus neoformans (Lodge et al., PNAS USA (1994), 91(25), 12008-12.) and Aspergillus fumigatus (Cook, W J et al., US Patent 20020025524 (2002), both in culture and animal models of infection.
Given the diverse role of myristoyl transferases and their association with a large variety of diseases and disorders, there is a need to find further myristoyl transferase inhibitors.
The present inventors have provided sulphonamide compounds which are inhibitors of N-myristoyl transferases.